1. Field of the Invention
Exemplary embodiments of the present invention relate to a vent structure for electromagnetic shielding; and, particularly, to a vent structure for electromagnetic shielding, which is conveniently mounted on a case of an electronic device, protects the electronic device by radiating heat generated inside the electronic device to the outside, and effectively attenuates electromagnetic waves generated inside the electronic device.
2. Description of Related Art
Electromagnetic waves are generated while an electromagnetic field, the intensity of which periodically changes, propagates in space.
Recently, with the development of communication technology, various electronic devices, ranging from small-sized electronic devices to middle and large-sized electronic devices, such as mobile phones, digital cameras, computers, and navigation devices, have been used in our daily lives.
Electromagnetic waves generated from such electronic devices have an effect on other electronic devices, and have become a factor that causes malfunction of devices due to mutual interference of electromagnetic waves between adjacent circuits.
Furthermore, as the spread of electromagnetic application devices rapidly increases, ordinary people, as well as workers in the manufacturing sector of electronic devices, are more frequently exposed to electromagnetic waves. Electromagnetic waves generated from an electronic device may have a bad influence on the human body. For example, electromagnetic waves may increase the temperature of tissue cells through a thermal effect, thereby weakening the immune function or causing genetic mutations.
For example, there is a report saying that microwave leakage from microwave ovens may cause cataracts or breast cancer, and there is a research result saying that electromagnetic waves from mobile phones may cause brain tumors or leukemia. In addition, there are many reports saying that electromagnetic waves may cause hypertension, headaches, or memory failure.
Therefore, the demand for an electromagnetic shielding structure, which prevents electromagnetic waves generated inside an electronic device from being discharged outside, or prevents electromagnetic waves from the outside from being propagated into a system, is gradually increasing.
FIG. 1 illustrates a vent for shielded enclosures disclosed in U.S. Pat. No. 5,401,914. In the vent for shielded enclosures, a waveguide having a small opening size is formed by inserting separate conductor plates 30, 32, 34, and 36 into a waveguide structure 25 through which the air passes, and the waveguide structure 25 is assembled into a structure for electromagnetic shielding through separate screws, thereby shielding electromagnetic waves while circulating internal and external air.
The structure of FIG. 1 relates to a vent for electromagnetic shielding having a pipe, which includes partitions or dividers, and a mounting plate or flange. The mounting plate or flange is a structure for connecting the shielding structure and the vent, and the partitions inside the pipe serve to divide the inner diameter of the pipe, through which electromagnetic waves and air pass, into dimensions required for attenuating the electromagnetic waves.
The pipe has a length such that it protrudes from the mounting plate or flange, and the pipe length may be larger than the inner diameter of the pipe. The mounting plate may be assembled to be electrically connected to the electromagnetic shielding structure, and may satisfy the continuity of the electromagnetic shielding structure. The air circulation between the inside and outside of the electromagnetic shielding structure may be performed through the pipe including the partitions, and the partitions inside the pipe may be assembled to divide all or a part of the pipe. In this case, the partitions inside the pipe may divide the inside of the pipe into four parts, while crossing each other at right angles. The diameter of the pipe, divided by the partitions inside the pipe, becomes smaller than the outer pipe diameter, and the entire length of the pipe may be shortened by the installation of the partitions, compared to when no partitions are installed. That is because the pipe diameter is reduced by the partitions installed inside the pipe, and the pipe length required for reducing electromagnetic waves is shortened by the reduction of the pipe diameter. In general, a pipe length which is four to five times as large as a pipe diameter is required to attenuate electromagnetic waves.
FIG. 2 illustrates a high performance EMC vent panel disclosed in U.S. Pat. No. 6,297,446. The high performance EMC vent is characterized in that a plurality of conducting plates 17 and 18, having a plurality of openings 11 therein, are stacked to be electrically connected to each other, and in that the openings in each conducting plate form a waveguide having a thickness suitable for shielding electromagnetic waves.
The structure of FIG. 2 relates to a vent for electromagnetic shielding, in which the plurality of conducting plates, each having the plurality of openings therein, are stacked to thus have a multilayered structure, and are electrically connected to form a waveguide structure capable of attenuating electromagnetic waves.
Since the waveguide structure formed by electrically connecting the plurality of conducting plates is used, the waveguide is thicker than a vent for electromagnetic shielding using a single conducting plate. Furthermore, the opening size may be designed to have a large value, due to electromagnetic wave attenuation characteristics based on the thickness of the waveguide.
In the structure of FIG. 2, the openings of the conducting plates forming the multilayered structure are aligned to have the same center, and form a path through which the air passes, and the conducting plates are electrically connected through a rivet or gasket positioned outside the conducting plates.
The above-described vents for electromagnetic shielding are designed to provide a path having a predetermined thickness such that electromagnetic waves are attenuated while propagating. In the case of FIG. 1, the opening through which the air passes is divided by the crossed partitions installed inside the circular waveguide. In the case of FIG. 2, the openings are formed by stacking the plurality of conducting plates having openings with a predetermined shape. The shielding performance of the vents for electromagnetic shielding is determined by the size of the opening and the length of the waveguide.
Therefore, in order to shield electromagnetic waves having a high frequency, the size of the opening through which the air passes should be set to a small value, and the thickness of the waveguide should be increased. In order to reduce the size of the opening through which the air passes or increase the thickness of the waveguide, the diameter of the circular waveguide should be decreased, and the thickness thereof should be increased, as in the case shown in FIG. 1. Furthermore, in the case of FIG. 2, the size of the opening in each conducting plate forming the multilayered structure should be decreased, and the thickness of the conducting plate or the number of conducting plates should be increased.
FIG. 3 illustrates a honeycomb vent panel for a vent for electromagnetic shielding, which is commercially sold by Holland Shielding System B.V. The honeycomb vent panel includes a frame 50 which is electrically connected to a honeycomb 40 having a shape similar to a honeycomb structure. In general, the honeycomb 40 includes a plurality of hexagonal cells having a predetermined thickness and positioned adjacent to each other, and the frame 50 is used for connecting the shielding structure to the honeycomb 40. Since the honeycomb, the frame, and the shielding structure must be electrically connected, conductive gaskets suitable for the respective connection portions are used. The honeycomb assembled to the frame is engaged with the electromagnetic shielding structure, and is used as a path through which the air is circulated.
In the case of the honeycomb used as a ventilation window having an electromagnetic shielding function, a waveguide four to five times longer than the maximum diameter of an opening is formed to a predetermined thickness such that electromagnetic waves are attenuated while passing through the waveguide. Furthermore, the thickness of the honeycomb should be increased in proportion with the opening size.
In the case of the commercial honeycomb, various products are sold according to the required electromagnetic shielding performance. Therefore, a suitable product may be selectively applied depending on the application. However, an assembly process using a frame suitable for a shielding structure to be applied is necessary, and a separate conductive gasket for electrical connection between the frame and the shielding structure must be included in a coupling portion and assembled.